Twenty-six avian infectious bronchitis (IB) viruses (IBV) were isolated from outbreaks in chickens in China between 1995 and 2004. They were characterized by comparison with twenty-six Chinese reference strains and five other IBV strains. Chinese IBVs, which were mainly nephropathogenic, were placed into seven genotypes. Fourteen Chinese IBV isolates were placed in genotype I, having small evolutionary distances from each other. Genotype II included 6 strains that were isolated in the 1990s in China. Genotype III consisted of eight Chinese isolates that showed close relationship with Korean IBV isolates. Another eight IBV isolates clustered in genotype IV and showed larger evolutionary distances. The Massachusetts serotype was present in China in 1990s and was in a separate genotype. Two isolates, HN99 and CK/CH/LHN/00I, which might be a reisolation of vaccine strains, clustered into genotype VI. Four Chinese IBV isolates formed another genotype and showed larger evolutionary distances from other Chinese IBV genotypes (genotype VII). IBVs in same genotypes showed more than 90% amino acid sequence similarities, whereas most of the viruses in different genotypes showed less than 90%. The results showed that IBVs in China came from genetic changes both in IBV populations that existed before the advent of vaccination and in the viruses that were introduced through live vaccines. IBVs showing various genetic differences are cocirculating in China.
1IntroductionPolymer bonded explosives (PBXs) [1][2][3][4] have usually been considered as ap articulate composite material containing the energetic materials hexahydro-1,3,5-trinitro-1,3,5-s-triazine (RDX) embedded in av iscoelastic polymer binder. PBXs are widely used in av ariety of conventional engineering and aerospace fields. As ah ighly-filled composite material, PBX exhibits complex physical and mechanical properties that are dependent on an umber of variables, such as temperature, strain rate, grains weight, and size distribution of grains, etc. [5,6].The Los Alamos National Laboratory (LANL) performed al ot of research on dynamic mechanical properties of PBXs. These results suggested that dynamic mechanical properties of PBX are strongly influenced by strain rate and temperature [7][8][9][10].A lso, the compressive strength is enhanced when increasing strain rate or decreasing temperature. PBX9501i sw idely researched at present,a nd the result illustrated that PBX9501 duringh igh-rate loading continue straining after the maximum flows tress have been achieved. Figure 1s hows the published compressive stress-strain data on PBX9501 currently known to the authors. When the peak strengths of PBX9501 are achieved, the flow strength beginst od ecline sharply because of damage accumulation. Graye tal. [11] revealed that at high-rate PBX 9501 fails via predominantly transgranular cleavage through the HMX crystals. Strains to failure remain almost constant throughout,a talevel of approximately 1-3 %. In fact, these damagep rocesses give rise to the enhanced sensitivity of PBX9501 followinga ni mpact.In the presented work, the micromechanical modelh as profited greatly from the theoretical analysis of Weng and co-workers [12-17] and considerable referencet ot heir work is madet hroughout this article. Their work is based on Eshelby's celebrateds olution of the stressa nd strain fields arising from the presence of an ellipsoidal inhomogeneity in an elastic matrix and Mori and Ta naka'se ffective medium theory,w hich was used to extendE shelby's analysis to larger valueso ff iller concentration [18,19].C lements and Mas have put forth am ethod that is ah ybrid of two Abstract:T he dynamic mechanical properties of PBX1314 and its binder are systematicallyi nvestigated. Based on split-Hopkinson pressure bar technique, the experimental results of PBX1314 and its binder are obtainedu nder high strain rate. Ac onstitutive theory is developed for modeling the mechanical response of dynamically loaded PBX1314 binder.T oa ccomplish this aim, the PBX1314 binderi sa ssayed by relaxation tests at different temperatures, in order to apply the time-temperature superposition principle (TTSP) and raise the masterc urves, based on WLF equation.The rate dependence of mechanical response of the polymer binder is accounted for by ag eneralized Maxwell viscoelasticity model. The basis for this work is Mori and Ta naka's effectivem ediumt heory.T he grains in this analysis are assumed to be spherical and uniformly distributed in the b...
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